The removal of toxic and hazardous materials from the environment is a growing concern. In particular, the removal of contaminants such as organic compounds and heavy metals from the soil is the focus of intense research. The contamination of groundwater and, ultimately, drinking water is the driving force behind the extensive research being conducted in order to remove toxic and hazardous contaminants from the soil.
Numerous techniques for the remediation of soil are disclosed in the art. One approach involves the excavation of soil followed by treating the soil with additives and chemicals to remove the contaminant. U.S. Pat. No. 5,674,176 to Pierce discloses the addition of phosphoric acid, monocalcium phosphate, monoammonium phosphate and diammonium either alone or in combination with Portland cement to excavated soil samples. U.S. Pat. No. 5,640,701 to Grant et al. disclose a method for removing radioactive contaminants from excavated soil by treating the soil with an extracting agent composed of potassium carbonate, potassium bicarbonate, sodium carbonate, sodium bicarbonate, sodium chloride, acetic acid, sodium hypochloride, ammonium carbonate, and ammonium bicarbonate. U.S. Pat. No. 5,193,936 to Pal et al. disclose treating excavated soil with a sulfate compound followed by a phosphate reagent.
The treatment of excavated soil has a number of disadvantages. First, it is expensive to operate excavating and trucking equipment needed to remove the contaminated soil. Second, the transportation of hazardous material is monitored by strict regulations. Finally, it has been shown in the art that some methods used to treat the excavated soil are not effective for the removal of heavy metals, such as lead, from the soil.
Another method involves the addition of additives or chemicals directly into the soil in order to convert the contaminant into a non-leachable form. U.S. Pat. No. 5,202,033 to Stanforth et al. disclose the addition of a phosphate, a carbonate, or a chemical reducing additive into the soil or waste. The contaminant is rendered nonhazardous, and is not removed from the soil. Indeed, Stanforth et al. disclose that the removal of the contaminant from the soil is lengthy and expensive.
The removal of contaminants from waste water has also been disclosed in the art. U.S. Pat. No. 4,289,594 to Aplaugh; U.S. Pat. No. 5,310,488 to Hansen et al.; U.S. Pat. No. 5,013,453 to Walker; U.S. Pat. No. 4,820,417 to Buchmeier; U.S. Pat. No. 4,272,494 to Ljubman et al.; U.S. Pat. No. 4,118,243 to Sandesara; U.S. Pat. No. 5,492,633 to Moniwa et al.; and U.S. Pat. No. 4,846,978 to Legget et al. disclose the removal of contaminants from waste water and aqueous solutions by chemical or physical means. These references, however, do not disclose the removal of contaminants from soil.
An alternative to treating excavated soil is in situ soil remediation. U.S. Pat. No. 5,769,961 to Peters et al. disclose a process for the in situ remediation of soil containing arsenic. The process involves contacting the soil with an aqueous extraction solution, directing the extractant solution through the soil so that the extractant solution interacts with the arsenic contaminant, and collecting the extractant solution containing the arsenic contaminant. Peters et al. disclose that iron and aluminum salts can be added to the extractant solution containing the arsenic contaminant in order to bring the arsenic contaminant out of solution. When an extractant, such as citric acid, is used in the process of Peters et al., the process is very inefficient with respect to arsenic removal because floc formation is inhibited by the citric acid. There is no disclosure in Peters et al. to remove the extractant from the solution prior to removing the arsenic by floc formation. Additionally, there is no disclosure in Peters et al. for using a membrane, such as a ceramic membrane, or an ion exchange resin to remove the arsenic contaminant from the extraction solution. Finally, Peters et al. does not disclose the mobilization of the contaminant in soil by electroremediation.
In light of the above it would be very desirable to have an efficient method for the in situ removal of a contaminant from soil. The present invention solves such a need in the art while providing surprising advantages. The present invention provides a method that effectively removes a contaminant from soil at an accelerated rate without having to treat excavated soil.